Need this program to handle invalid input (Letters specifically)

Thank you

import java.util.Scanner;

public class PocketMain {

public static void main(String args[]) throws NoSuchCoin

{

Pocket pocket = new Pocket(); //loop goes on until valid input

boolean exit =false;

while(!exit)

{

System.out.println("Choose one operation: "

+ "1.Add a coin (must specify type) "

+ "2.Remove a coin (must specify type) "

+ "3.Display a coin count "

+ "4.Display a total value in the pocket "

+ "5.exit the program");

Scanner sc = new Scanner(System.in);

int choice = sc.nextInt();

switch(choice){

case 1:

System.out.println("Enter type of coin "

+ "1.Dime "

+ "2.Nickle "

+ "3.Penny "

+ "4.Quarter");

int selection =sc.nextInt();

switch(selection){ //case executes depending on user's choice

case 1:pocket.addCoin( new Dime());

System.out.println("dime added to pocket successfully");

break;

case 2:pocket.addCoin(new Nickle());

System.out.println("Nickle added to pocket successfully");

break;

case 3:pocket.addCoin(new Penny());

System.out.println("Penny added to pocket successfully");

break;

case 4:pocket.addCoin(new Quarter());

System.out.println("Quarter added to pocket successfully");

break;

default:throw new NoSuchCoin();

}

break;

case 2:

System.out.println("Enter type of coin "

+ "1.Dime "

+ "2.Nickle "

+ "3.Penny "

+ "4.Quarter");

selection =sc.nextInt();

switch(selection){

case 1:pocket.removeCoin(Coin.DIME);

System.out.println("Dime removed from pocket successfully");

break;

case 2:pocket.removeCoin(Coin.NICKLE);

System.out.println("Nickle removed from pocket successfully");

break;

case 3:pocket.removeCoin(Coin.PENNY);

System.out.println("Penny removed from pocket successfully");

break;

case 4:pocket.removeCoin(Coin.QUARTER);

System.out.println("Quarter removed from pocket successfully");

break;

default:throw new NoSuchCoin();

}

break;

case 3:

System.out.println("Enter type of coin "

+ "1.Dime "

+ "2.Nickle "

+ "3.Penny "

+ "4.Quarter");

selection =sc.nextInt();

switch(selection){

case 1:System.out.println("Dimes:"+pocket.countCoins(Coin.DIME));

break;

case 2:System.out.println("Nickles:"+pocket.countCoins(Coin.NICKLE));

break;

case 3:System.out.println("Pennys:"+pocket.countCoins(Coin.PENNY));

break;

case 4:System.out.println("Quarters:"+pocket.countCoins(Coin.QUARTER));

break;

default:throw new NoSuchCoin();

}

break;

case 4:

System.out.println("Total value of the Pocket:"+pocket.totalValue());

break;

case 5:

exit=true;

break;

default : System.out.println("Invalid input exiting program");

exit=true;

}

}

}

}